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E. coli Up Close and Personal: Scientific Rockstar and Public Enigma


This is an article created as guest post for Kitchen Table Science.

It seems nothing puts fear in the hearts of the masses like mentioning E. coli. Most think of the disease-causing germ that contaminates everything from spinach to beef. I agree the strain Escherichia coli O157:H7 and its cousins O26, O145, STEC O104:H4, and others, are a wretched bunch that give the whole species a bad reputation. What makes these strains so vile are the extra proteins encoded within their genome. For example, E. coli O157:H7 has a larger genome coding for 5561 proteins while the parent strain E. coli W codes for 4739 proteins. Thus is the life of a bacterium. The fact there are so many bacteria means they are usually in close proximity to each other. Physical contact between bacteria, not just those of the same species, allows for the transfer of genetic material between two cells (horizontal gene transfer); the closest thing to sexual reproduction you will find for prokaryotes. If the genes transferred to the recipient give it an advantage or new ability that helps it compete and thrive in its environment, they will remain in the genome. Otherwise, they will be discarded after genome compaction.

Most E. coli are completely harmless and, in fact, beneficial. If the general public knew more than what was broadcasted on the 24 hour news channels, they would see the tiny rockstar scientists have known about for some time now. Beginning in earnest in the 1950s, E. coli is easily cultured in laboratories and very cheaply. Its quick generation time (20 min. at optimum temperature) made it a great model organism to study in many fields of science and medicine. This organism is the work horse of biotechnology due to the relative ease of manipulating its genome or adding complete genetic circuits into the cell using plasmids.

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Even after 50 years of intense research, E. coli still holds many unknowns out of the reach of our knowledge. Like all other sequenced genomes, there are a number of “hypothetical proteins” and “proteins of unknown function”. This means by our best abilities, we can locate parts of the genome that code for proteins, however, this doesn’t mean we are able to understand the function of a particular protein.

Image courtesy of Predrag Radivojac. Thanks, Pedra.

The above shows just how much work is left to understand the biological capabilities of Mother Nature. Short version: over 40 gene sequences in databases, but the number of which that we know what the function is holding steady around 500,000 and the number of solved protein structures is over 100,000. This is a growing gap between the known and unknown.

 Where would we be without E. coli?

One advantage of E. coli is their effect on our immune system. Some may find this counter-intuitive, but E. coli can lower the workload of our immune system when pathogens are present, especially in the intestine. When E. coli attach to the GI wall, it changes the acidity of the lining thus making infection from other bacteria less likely. Another benefit is in overall digestion. E. coli promotes better breakdown of food thus preventing accumulation of waste which is a major cause of bloating and constipation.

Many outside the scientific community may not be aware of how integral E. coli are to the advancement of many fields including medicine, pharmacology, biology, and even human physiology. Another reason to not believe the hype.

Constantly attacked by immune system would make me a pathogen, too.


This week, a new study published in PLOS Pathogens reported how otherwise benign, commensal E. coli can evolve before our eyes into a malicious pathogen.  In this study, researchers cultured E. coli with the mouse immune cells that essentially eat them when found in the body; the macrophages. The co-culture was diluted daily. This would give the bacterial cells a constant source of fresh nutrients. Under constant threat of attack by the immune cells, the E. coli were under ‘continual selective pressures’.  A few days of these living conditions caused positive selection of genetic mutations that now allowed the bacteria to evade macrophages. Seven new types of E. coli were identified through this screen and the genomes were sequenced to find the sources of the mutations.

Here are some problems…

E. coli were continually in contact with macrophages in this study. This is very unrealistic and the authors acknowledge this, saying:

We note that in the context of a real infection repeated contact with macrophages will not likely occur with a similar period as the one in this experimental setup.

Another quick problem noticed is that these bacterial cells were growing in an otherwise optimal environment; nutrients were replenished everyday. Again, this is not going to happen in nature. To put this into focus, it would be like winning the lottery jackpot every drawing for a month. In other words, it is not likely.

Under these experimental conditions, researchers were able to force these bacteria to change or die. As in every other challenge faced for over 2 billion years, the E. coli rose to the challenge and did so quickly.

So, congratulations to the authors. You did the expected and got the expected. But hold on; this study did do something really nice. It allows researchers to see the kind of mutations occurring that allow seemingly nice bacteria to become less so. Yet again, we learn from bacterial superstar, E. coli.

Useful Products Engineered into E. coli “Poop” (Thank Goodness)


I can’t sit back and let the internet become saturated with misleading phrasing regarding by-products genetically engineered into E. coli metabolism. The latest sensation stems from the commercial production of the artificial sweetener aspartame. It was reported this week, well…read it for yourself (notice the language used):

This scientific jargon obfuscates (perhaps deliberately) a truly disturbing process:
1.) ‘Cloned microorganisms’ (which the patent later reveals to be genetically modified E. coli) are cultivated in tanks whose environments are tailored to help them thrive.
2.) The well-fed E. coli cultures defecate the proteins that contain the aspartic acid-phenylalanine amino acid segment needed to make aspartame.
3.) The proteins containing the Asp-Phe segments are ‘harvested’ (i.e. lab assistants collect the bacteria’s feces).
4.) The feces are then treated. This includes a process of methylation (adding an excess of the toxic alcohol, methanol, to the protected dipeptide).

While common sense dictates that this abomination doesn’t belong anywhere near our bodies, the patent’s authors made no secret about their belief that aspartame constitutes a safe and nutritious sweetener:

Source

It was picked up on the UPI under “Science News” with a headline reading:

The use of the words ‘poop’, ‘feces’, ‘defecate’, and ‘excrement’ is truly unfortunate and used to sensationalize the process. Natural News has an agenda, or several agendas. First they are against genetic modifications to living organisms even though almost all discoveries and breakthroughs in modern medicine can be contributed to some form of genetic modification. Second, they are publicly against the use of aspartame in commercial products.

The truth about E. coli ‘poop’

First, E. coli do not ‘poop’ in the sense a human can relate. These are single-celled organisms and are rather leaky to certain molecules naturally. E. coli produce by-products, not poop. Metabolic end products are considered waste to the E. coli cell, but these natural end products include carbon dioxide, hydrogen gas, acetate (vinegar), and water. Their poop doesn’t sound so bad now does it?

The evolution of E. coli ‘poop’

E. coli has been the organism of choice for decades in myriad research areas. Simple genetic modifications like gene deletion and gene insertion are the norm and can easily be performed in a lab. Scientists and doctors have used this technique to engineer novel strains of E. coli that tweaks their metabolism to produce useful products for the general public. One great example occurred in 1978 by Herbert Boyer who inserted the gene for human insulin into E. coli. Recombinant insulin was approved by the FDA in 1982 and is now the source of 70% of the insulin sold today.

Human growth factor is another by-product engineered into E. coli to treat different forms of dwarfism. For hemophiliacs, E. coli are utilized to produce missing clotting factors like tissue plasminogen activator and factor VIII. It should be noted that before producing these therapeutics in E. coli, they were harvested from cadavers. Patients with immunodeficiency can receive recombinant interferon, used to treat viral infections, produced in bacteria.

E. coli and other bacteria are used in other industries as well. They have been modified to produce large amounts of succinate, a precursor for the solvent 1,4-butanediol. It can then be used to make some plastics and even Spandex. E. coli are also used in the production of polyhydroxybutyrate, or PHB, for the production of plastics. E. coli is also used for production of polyamines for synthesis of polyamide plastics.

Over the past decade, a lot of research has taken place in the field of renewable energy. One approach to lessen our dependence on foreign oil is the microbial conversion of cellulosic (non-food) plant material into viable fuels like ethanol and butanol. This task has given E. coli and other microbes ‘poop potential’. Through genetic engineering and synthetic biology techniques, E. coli can produce large amounts of free fatty acids which are one catalytic step away from the same diesel fuel derived from petroleum. E. coli is also engineered to produce precursors for jet fuel.

In this post, I have focused on only one microbe, E. coli, since this was the bacterium sensationalized this week in the press.

Simplistic view of bacteria in your intestine: a first draft illustration


bacterial art, microbiology, microbiome, science, science art
View of different types of bacteria within the lumen of the human intestine.